1. Technical Field
The present invention relates to a slip prevention member for turntables.
2. Description of the Related Art
Because of an increasing amount of data being stored, the methods of storing data are recently changing from electric to optical methods. In the case of the electric method, data is stored by varying the electric capacity and the electric resistance of a place for storing data. Such variation is electrically read. In the case of the optical method, data is stored by varying transmissivity, reflexibility, phase, polarization, etc. of light. Such variation is read using laser beams.
An optical disk is an optical memory medium used by the optical method. A digital audio disk (DAD), which is generally referred to as a CD and used to reproduce audio, and a digital video disk (DVD) are representative examples of optical disks. The optical disk is placed onto a turntable which is rotated by a spindle motor and reflects a laser beam radiated from a pick-up unit which is moved in the radial direction of the optical disk. The pick-up reads data using reflexibility of the reflected laser beam or a variation in the phase or polarization of the beam when it is reflected.
However, because the turntable rotates at high speed, the disk placed on the turntable may be removed from or slipped with respect to the turntable, resulting in the problem of the pick-up unit not being able to precisely read the data. In an effort to overcome the problem of a disk slip, a technique in which a slip prevention member is attached to the upper surface of the turntable onto which the disk is placed is being developed or used. A representative example of this technique was proposed in [Patent document 1].
FIG. 1 is a sectional view of a disk chucking device having a slip prevention member 30 disclosed in [Patent document 1]. In this conventional technique, the slip to prevention member 30 made of a rubber sheet is attached to an upper surface of a turntable 20 which is rotated by a drive unit 10. A disk 40 is placed onto the slip prevention member 30. Thus, a slip of the disk 40 is prevented by frictional force between the slip prevention member 30 and the disk 40.
However, the rubber sheet is an environmentally toxic material and the use thereof is thus restricted. Hence, use of the slip prevention member 30 imposes a burden of environmental pollution.
In an effort to overcome the above problem, there was an attempt to produce the slip prevention member 30 using silicone material which can conduct the same function as the rubber sheet. However, because the hardness of the silicon material is very low, it becomes very difficult to attach the slip prevention member 30 to the turntable 20. That is, typically, the slip prevention member 30 is manually attached to the turntable 20 using double-sided adhesive tape. In the case where the slip prevention member 30 is made of silicone material, because the hardness thereof is too low to maintain the original shape thereof, it is very difficult to attach the slip prevention member 30 to the turntable 20 at the correct position such that it is in close contact with the turntable 20.
Moreover, in the case of the silicone material having low hardness, the surface precision thereof is also low. Hence, a surface shaking phenomenon of the disk may be induced, resulting in occurrence of vibrations and noise when the disk rotates at high speed.    [Patent document 1] Japanese Patent Laid-open Publication No. Heisei. 5-135464